In response to CDC RFA-DD-07-007 (Implementing Surveillance to Determine Prevalence of the Autism Spectrum Disorders (ASD)...in Early Childhood Populations), we propose CA-MECA, to be conducted under the leadership of the California Department of Health Services (DHS) and in partnership with Kaiser Permanente of Northern California (KPNC), and multiple health and service providers in Santa Clara County (SCC), California. Our primary goal is to establish a scientifically rigorous, multi-source surveillance system to accurately determine the population-based prevalence of ASD in young children (<4 years old) for two birth cohort years (2005-2006) in SCC, which has ~26,000 births/year and a very diverse population. Doing so is relevant to CDC's goal to prevent birth defects and developmental disabilities and improve the health of people with disabilities. There are three components to the CAMECA proposal that reflect our specific aims: 1) To identify young children (<48 months) with possible or definite autism in the county born in the two target years, we will work with the local regional center for the developmentally disabled, community clinics, and specialty providers. Records will be abstracted to collect data to determine final surveillance case status by expert review and to describe characteristics of the children with ASD. Additional data will be obtained from birth certificates. Both current and birth residence prevalence estimates will be calculated. 2) To identify possible gaps in the surveillance system and to reach an under-served segment of the population, we will conduct routine screening for developmental disabilities and ASD in 18-30 month old children born in 2006 at two pediatric clinics that serve a lower income, primarily Hispanic population, with appropriate referrals for clinical evaluation. After linkage to the surveillance system, we will compare prevalence in the screened sub-group to those born in 2005 and seen at the same clinics but not screened, to evaluate completeness of overall prevalence estimates and to provide a more accurate estimate of prevalence in a Hispanic population. 3) To increase awareness and early referrals for autism evaluations, we will conduct outreach and education to general pediatricians and other relevant community groups, assembling and convening a community advisory board to assist us. The two data collection components include on-going quality control, and will be evaluated for completeness, accuracy and feasibility of wider application. Reports will be widely distributed. Data from the CA-MECA project will be valuable for obtaining accurate counts of young children with ASD to track changes over time, to plan and deliver services for affected children and their families, to uncover risk factors for ASD, and to identify underserved groups, as well as providing information to improve early screening and diagnostic practices.